In the Linux kernel, the following vulnerability has been resolved:
RDMA/siw: Reject MPA FPDU length underflow before signed receive math
A malicious connected siw peer can send an iWARP FPDU whose MPA length
field (c_hdr->mpa_len, 16 bit big-endian, peer-controlled) is smaller
than the fixed DDP/RDMAP header for the announced opcode. Soft-iWARP
parses the full header in siw_get_hdr() based on iwarp_pktinfo[opcode]
.hdr_len, but never compares mpa_len against that header length.
siw_tcp_rx_data() then derives
srx->fpdu_part_rem = be16_to_cpu(mpa_len) - fpdu_part_rcvd
+ MPA_HDR_SIZE;
where fpdu_part_rcvd equals iwarp_pktinfo[opcode].hdr_len at this
point. For a tagged WRITE (hdr_len 16, MPA_HDR_SIZE 2) the smallest
on-wire mpa_len of 0 yields fpdu_part_rem = -14, and any mpa_len below
hdr_len - MPA_HDR_SIZE underflows to a negative int.
The signed value then flows into siw_proc_write()/siw_proc_rresp() as
bytes = min(srx->fpdu_part_rem, srx->skb_new);
is handed to siw_check_mem() as an int len (whose interval check
addr + len > mem->va + mem->len is satisfied for a valid base when
len is negative), and reaches siw_rx_data() -> siw_rx_kva() /
siw_rx_umem() -> skb_copy_bits() as a signed copy length. The header
copy branch in skb_copy_bits() promotes that to size_t, producing a
multi-gigabyte read.
KASAN under a KUnit harness that drives the real kernel TCP receive
path -- a loopback AF_INET socketpair, the malformed FPDU written via
kernel_sendmsg, sk_data_ready firing in softirq, tcp_read_sock
dispatching to siw_tcp_rx_data -- reports:
BUG: KASAN: use-after-free in skb_copy_bits+0x284/0x480
Read of size 4294967295 at addr ffff888...
Call Trace:
skb_copy_bits
siw_rx_kva
siw_rx_data
siw_check_mem
siw_proc_write
siw_tcp_rx_data
__tcp_read_sock
siw_qp_llp_data_ready
tcp_data_ready
tcp_data_queue
Add the missing invariant at the earliest point where the peer header
is fully assembled. iwarp_pktinfo[*].hdr_len - MPA_HDR_SIZE is exactly
the value the siw transmitter uses as the minimum mpa_len for each
opcode (drivers/infiniband/sw/siw/siw_qp.c:33), so this matches the
protocol contract. Out-of-range FPDUs terminate the connection with
TERM_ERROR_LAYER_LLP / LLP_ETYPE_MPA / LLP_ECODE_FPDU_START -- which
is RFC 5044 Section 8 error code 3 ("Marker and ULPDU Length fields
do not agree on the start of an FPDU"), the correct framing-error
class for this inconsistency.
RDMA/siw: Reject MPA FPDU length underflow before signed receive math
A malicious connected siw peer can send an iWARP FPDU whose MPA length
field (c_hdr->mpa_len, 16 bit big-endian, peer-controlled) is smaller
than the fixed DDP/RDMAP header for the announced opcode. Soft-iWARP
parses the full header in siw_get_hdr() based on iwarp_pktinfo[opcode]
.hdr_len, but never compares mpa_len against that header length.
siw_tcp_rx_data() then derives
srx->fpdu_part_rem = be16_to_cpu(mpa_len) - fpdu_part_rcvd
+ MPA_HDR_SIZE;
where fpdu_part_rcvd equals iwarp_pktinfo[opcode].hdr_len at this
point. For a tagged WRITE (hdr_len 16, MPA_HDR_SIZE 2) the smallest
on-wire mpa_len of 0 yields fpdu_part_rem = -14, and any mpa_len below
hdr_len - MPA_HDR_SIZE underflows to a negative int.
The signed value then flows into siw_proc_write()/siw_proc_rresp() as
bytes = min(srx->fpdu_part_rem, srx->skb_new);
is handed to siw_check_mem() as an int len (whose interval check
addr + len > mem->va + mem->len is satisfied for a valid base when
len is negative), and reaches siw_rx_data() -> siw_rx_kva() /
siw_rx_umem() -> skb_copy_bits() as a signed copy length. The header
copy branch in skb_copy_bits() promotes that to size_t, producing a
multi-gigabyte read.
KASAN under a KUnit harness that drives the real kernel TCP receive
path -- a loopback AF_INET socketpair, the malformed FPDU written via
kernel_sendmsg, sk_data_ready firing in softirq, tcp_read_sock
dispatching to siw_tcp_rx_data -- reports:
BUG: KASAN: use-after-free in skb_copy_bits+0x284/0x480
Read of size 4294967295 at addr ffff888...
Call Trace:
skb_copy_bits
siw_rx_kva
siw_rx_data
siw_check_mem
siw_proc_write
siw_tcp_rx_data
__tcp_read_sock
siw_qp_llp_data_ready
tcp_data_ready
tcp_data_queue
Add the missing invariant at the earliest point where the peer header
is fully assembled. iwarp_pktinfo[*].hdr_len - MPA_HDR_SIZE is exactly
the value the siw transmitter uses as the minimum mpa_len for each
opcode (drivers/infiniband/sw/siw/siw_qp.c:33), so this matches the
protocol contract. Out-of-range FPDUs terminate the connection with
TERM_ERROR_LAYER_LLP / LLP_ETYPE_MPA / LLP_ECODE_FPDU_START -- which
is RFC 5044 Section 8 error code 3 ("Marker and ULPDU Length fields
do not agree on the start of an FPDU"), the correct framing-error
class for this inconsistency.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
|
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Fixes
Solution
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Workaround
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References
History
Mon, 20 Jul 2026 14:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
cvssV3_1
|
Sun, 19 Jul 2026 16:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: RDMA/siw: Reject MPA FPDU length underflow before signed receive math A malicious connected siw peer can send an iWARP FPDU whose MPA length field (c_hdr->mpa_len, 16 bit big-endian, peer-controlled) is smaller than the fixed DDP/RDMAP header for the announced opcode. Soft-iWARP parses the full header in siw_get_hdr() based on iwarp_pktinfo[opcode] .hdr_len, but never compares mpa_len against that header length. siw_tcp_rx_data() then derives srx->fpdu_part_rem = be16_to_cpu(mpa_len) - fpdu_part_rcvd + MPA_HDR_SIZE; where fpdu_part_rcvd equals iwarp_pktinfo[opcode].hdr_len at this point. For a tagged WRITE (hdr_len 16, MPA_HDR_SIZE 2) the smallest on-wire mpa_len of 0 yields fpdu_part_rem = -14, and any mpa_len below hdr_len - MPA_HDR_SIZE underflows to a negative int. The signed value then flows into siw_proc_write()/siw_proc_rresp() as bytes = min(srx->fpdu_part_rem, srx->skb_new); is handed to siw_check_mem() as an int len (whose interval check addr + len > mem->va + mem->len is satisfied for a valid base when len is negative), and reaches siw_rx_data() -> siw_rx_kva() / siw_rx_umem() -> skb_copy_bits() as a signed copy length. The header copy branch in skb_copy_bits() promotes that to size_t, producing a multi-gigabyte read. KASAN under a KUnit harness that drives the real kernel TCP receive path -- a loopback AF_INET socketpair, the malformed FPDU written via kernel_sendmsg, sk_data_ready firing in softirq, tcp_read_sock dispatching to siw_tcp_rx_data -- reports: BUG: KASAN: use-after-free in skb_copy_bits+0x284/0x480 Read of size 4294967295 at addr ffff888... Call Trace: skb_copy_bits siw_rx_kva siw_rx_data siw_check_mem siw_proc_write siw_tcp_rx_data __tcp_read_sock siw_qp_llp_data_ready tcp_data_ready tcp_data_queue Add the missing invariant at the earliest point where the peer header is fully assembled. iwarp_pktinfo[*].hdr_len - MPA_HDR_SIZE is exactly the value the siw transmitter uses as the minimum mpa_len for each opcode (drivers/infiniband/sw/siw/siw_qp.c:33), so this matches the protocol contract. Out-of-range FPDUs terminate the connection with TERM_ERROR_LAYER_LLP / LLP_ETYPE_MPA / LLP_ECODE_FPDU_START -- which is RFC 5044 Section 8 error code 3 ("Marker and ULPDU Length fields do not agree on the start of an FPDU"), the correct framing-error class for this inconsistency. | |
| Title | RDMA/siw: Reject MPA FPDU length underflow before signed receive math | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-07-20T13:43:20.335Z
Reserved: 2026-07-19T07:54:57.033Z
Link: CVE-2026-64102
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.